1. Field of the Invention
The subject invention relates to composite metal and wood doors and, more particularly, composite doors that have a high fire rating as well as a high degree of sound attenuation.
2. Description of the Prior Art
Many types of wood doors have been developed with improved insulation properties. Frequently, such doors have a wooden subframe with an insulative foam core. Examples are found in U.S. Pat. Nos. 5,361,522 and 5,218,807. Although these doors had improved thermal insulative properties, they were not fire retardant and could not be used in applications where high fire ratings were required.
Doors having fire retardant qualities also have been developed. Such fire-retardant doors have various designs. Examples that employ a fire-retardant core or that incorporate fire-retardant chemicals are shown in U.S. Pat. Nos. 4,203,255 and 4,746,555. Still other doors have been designed with the objective of increasing sound attenuating properties. Such doors have a variety of structures and designs, some examples of which are shown in U.S. Pat. Nos. 4,998,598 and 5,416,285. However, it has been generally found that doors that have been designed singularly with regard to fire-retardant properties or with regard to sound attenuating properties, generally do not afford high performance in both respects.
In some instances, it has been desirable to have a door with combined properties of a given fire rating and a given sound attenuation. Examples that are directed to both of these objectives are shown in U.S. Pat. Nos. 5,422,170 and 5,417,029. With particular regard to fire-retardant, sound attenuating doors, it has been desirable to improve the appearance of these doors by adding a wood or other decorative laminate. However, it has been found that the addition of such a laminate to doors of such prior art designs has frequently tended to compromise the fire retarding or sound attenuating properties of the doors.
Accordingly, there was a need in the prior art for a door with improved aesthetics, but that also had high tolerance to fire and was effective in attenuating noise.